Hi all,
I was wondering if anyone knew a good/safe way to update a single column in a table that could contain upto 8 million rows...
simple command like:
UPDATE set blah=foo where bar=XXX;
I will be running this on tables being written to and tables that have already been created.
... (3 Replies)
Hello.
I'm not sure how I can get around this, or what I am doing wrong, but I need some help. :)
I want to do an select query looking like this:
SELECT venue, SUM( amount )
FROM IWD
WHERE venue = 'Foxy Hollow'
Unfortunately I need to have spaces in the names in these fields,
is... (10 Replies)
Hi All,
I need to update 2 rows in my file. But i can do only one row update by sed command. Please help me how can i change mutltiple rows in single sed commana
my i/p file: (example.txt)
record
integer (10) present_id;
string (10) first_name;
string (10) last_name;
string... (2 Replies)
Hello,
Met a problem when I tried to insert rows to MySQL database from an old book that fits my learning level (MySQL and Perl for the Web, by Paul DuBois, 2001). First, under mysql console I created a database: webdb and the table: todo. Then I draft the perl-cgi script to have online page.... (0 Replies)
I feel stupid for asking this because it seems that MYSQL code isn't working the way that I think it should work.
Basically I wrote code like this:
select * from `Test_DC_Trailer` HAVING max(DR_RefKey);
Where the DR_RefKey is a unique numeric field that is auto iterated (like a primary key)... (7 Replies)
Hi, i want to create a table automatically based on another table (sms_key).
For example;
If user create a new row with sms_keyword field: IRC then a table created automatically (with some field on it, like: name, ph_number, messages).
select * from sms_key;
+-------------+
|... (1 Reply)
Dear community,
I have to split string in table and list all values. I'll skip the code and jump directly to mysql query.
This is the table:
category title
======= =======
7,3 title 1
1,3 title 2
1,2,3 title 3
Now, what I need is split category into single... (2 Replies)
Right I have a MYSQL database with table1 with 3 columns, colA, colB and colC. I want to combine the data in the 3 columns into a 4th column names col_comb. Here's the SQL command that works:
UPDATE table1 SET `col_comb` = CONCAT( `colA` , ' - ', `colB` , ', ', `colC` );
So now I want this... (5 Replies)
Discussion started by: barrydocks
5 Replies
LEARN ABOUT DEBIAN
bup-margin
bup-margin(1) General Commands Manual bup-margin(1)NAME
bup-margin - figure out your deduplication safety margin
SYNOPSIS
bup margin [options...]
DESCRIPTION
bup margin iterates through all objects in your bup repository, calculating the largest number of prefix bits shared between any two
entries. This number, n, identifies the longest subset of SHA-1 you could use and still encounter a collision between your object ids.
For example, one system that was tested had a collection of 11 million objects (70 GB), and bup margin returned 45. That means a 46-bit
hash would be sufficient to avoid all collisions among that set of objects; each object in that repository could be uniquely identified by
its first 46 bits.
The number of bits needed seems to increase by about 1 or 2 for every doubling of the number of objects. Since SHA-1 hashes have 160 bits,
that leaves 115 bits of margin. Of course, because SHA-1 hashes are essentially random, it's theoretically possible to use many more bits
with far fewer objects.
If you're paranoid about the possibility of SHA-1 collisions, you can monitor your repository by running bup margin occasionally to see if
you're getting dangerously close to 160 bits.
OPTIONS --predict
Guess the offset into each index file where a particular object will appear, and report the maximum deviation of the correct answer
from the guess. This is potentially useful for tuning an interpolation search algorithm.
--ignore-midx
don't use .midx files, use only .idx files. This is only really useful when used with --predict.
EXAMPLE
$ bup margin
Reading indexes: 100.00% (1612581/1612581), done.
40
40 matching prefix bits
1.94 bits per doubling
120 bits (61.86 doublings) remaining
4.19338e+18 times larger is possible
Everyone on earth could have 625878182 data sets
like yours, all in one repository, and we would
expect 1 object collision.
$ bup margin --predict
PackIdxList: using 1 index.
Reading indexes: 100.00% (1612581/1612581), done.
915 of 1612581 (0.057%)
SEE ALSO bup-midx(1), bup-save(1)BUP
Part of the bup(1) suite.
AUTHORS
Avery Pennarun <apenwarr@gmail.com>.
Bup unknown-bup-margin(1)
03-25-2014
) so i need to edit all his entries to get new section ID.